The present invention relates generally to apparatus for processing whole blood, and more specifically to blood fractionation apparatus for separating and collecting a desired blood component, such as plasma.
Various methods and apparatus have been developed for the continuous flow processing of whole blood, wherein whole blood is taken from a live donor, a desired blood component is separated and collected, a replacement fluid is added to the processed blood, and the processed blood is returned to the donor. Blood components typically collected using such processing include plasma (plasmapheresis), white blood cells (leukopheresis) and platelets (plateletpheresis).
Continuous flow blood processing apparatus maybe of the centrifugal type, wherein the differing density of the collected blood component causes the component to congregate for collection at a particular radial distance in a centrifuge, or may be of the filter type, wherein the particle size of the collected component allows only that component to pass through a filter membrane into a collection chamber. Filter type apparatus is generally preferable for continuous flow plasmapheresis applications, since such apparatus does not require complex rotating machinery and is more compact and less costly to manufacture.
One form of filter which is particularly attractive for use in plasmapheresis apparatus utilizes a plurality of parallel microporous hollow fibers arranged side-by-side in the form of a bundle within a hollow cylinder. As whole blood is caused to flow through the fibers the plasma component passes through the walls of the fibers to the surrounding container, which forms a collection chamber from which the component is transported to a collection bag. A preferred construction and method of manufacture of such a hollow fiber filter is shown in the copending application of Robert Lee and William J. Schnell, entitled, "Microporous Hollow Fiber Membrane Assembly and Its Method of Manufacture", Ser. No. 278,913, filed June 29, 1981.
To preclude operation in the event of a mechanical malfunction, the plasmapheresis apparatus typically includes a plurality of devices which monitor the fluid flow system. One such device may be a bubble detector of either the light or ultrasonic type which monitors a particular segment of the tubing for fluid absence, such as might result from a bubble or air in the system. Another such monitor device monitors for either excessive negative pressure at the inlet of the system or to excessive positive pressure downline of the whole blood pump.
In the operation of plasmapheresis apparatus it is necessary that the apparatus operate in various modes, including a purge mode for displacing air from the system, a run mode for performing the plasmapheresis process, and a reinfuse mode for returning fluid to the patient. The apparatus therefore requires a control system which allows the selection of these modes quickly and without undue attention on the part of the operator. The control circuit should include necessary interlocks to prevent inadvertent mis-selection of an operating mode, and should condition all elements of the processing apparatus, including the bubble detector and pressure monitoring devices.
The plasmapheresis apparatus should also include a failsafe control circuit independent of the control circuit which monitors all functions and removes power from the pump motors when a stop is called for by the control circuit and not responded to by the pump motor.
The present invention provides control systems for blood fractionation apparatus such as that utilized for plasma separation and collection wherein a user-cancellable audible alarm is provided for a first category of system parameters, a non-cancellable visual alarm and interruption of operation are provided for a second category of parameters, and wherein the operating mode and the operation of the pumps are continuously and independently monitored and operation of the system is terminated after a predetermined delay in the event of an uncorrected malfunction.
In addition, the plasmapheresis apparatus described herein provides for convenient connection of an auxiliary collection monitoring and replacement fluid ratio control apparatus such as that described in the copending applications of Arnold C. Bilstad and John T. Foley, entitled, "Blood Fractionation Apparatus Having Collected Volume Display System", Ser. No. 330,899; "Blood Fractionation Apparatus Having Collection Rate Display System", Ser. No. 330,901; and "Blood Fractionation Apparatus Having Replacement Fluid Ratio Control System", Ser. No. 330,900; all assigned to the present assignee and filed concurrently herewith. As described in these applications this apparatus provides an exchange mode wherein an operator-selected ratio between the volume of plasma collected and the volume of replacement fluid added is automatically maintained; and an autologous mode wherein the replacement pump is connected to withdraw fluid from the collection container for secondary processing and return to the donor, and the operating rate of the pump is automatically varied to maintain a constant plasma level in the collection container.